In an existing illumination device, a low power LED module is usually used as alight source. In a general case, when this type of illumination device is applied in an outdoor environment, the requirement for a certain level of IP protection needs to be met. In order to achieve a good protection, one solution in the prior art is to use a single-side potting method, viz. a PCB board loaded with a LED chip is first placed in a half housing of a housing, the other half housing is then joined with said half housing to form an integral housing, later, a potting glue is pot into the housing via an potting hole formed on one half housing, and air is discharged from an exhaust hole also formed on said half housing. After the potting glue gets solid, the housing achieves a better protection effect to meet the requirement for the level of IP protection. However, the drawback of this method lies in that, the potting glue may leak from the slim between the two half housings, and the leaking potting glue has a negative effect on the aesthetic properties of the housing. If the potting glue in the slim is pull off after getting solid, it will possibly results in a decrease in the leakproofness of the housing, which affects the IP protection effect adversely. Another solution in the prior art is that two housing members are welded together via ultrasonic welding after being joined together, which obtains favorable leakproofness. However, the high frequency vibration of ultrasonic might damage the LED chip.